A microarray is essentially a two-dimensional support or sheet wherein different portions or cells (sectors) of the support or sheet carry different biomolecules or elements, such as, nucleotides, polynucleotides, peptides, polypeptides, saccharides or polysaccharides, bound thereto. Microarrays are similar in principle to other solid phase arrays except that assays involving such microarrays are performed on a smaller scale, allowing many assays to be performed in parallel. Microarrays have been used for a number of analytical purposes, typically in the biological sciences.
Biochemical molecules on microarrays have been synthesized directly at or on a particular cell (sector) on the microarray, or preformed molecules have been attached to particular cells (sectors) of the microarray by chemical coupling, adsorption or other means. The number of different cells (sectors) and therefore the number of different biochemical molecules being tested simultaneously on one or more microarrays can range into the thousands. Commercial microarray plate readers typically measure fluorescence in each cell (sector) and can provide data on thousands of reactions simultaneously thereby saving time and labor. A representative example of a patent in the field is U.S. Pat. No. 5,545,531.
Currently, two dimensional arrays of macromolecules are made either by depositing small aliquots on flat surfaces under conditions which allow the macromolecules to bind or be bound to the surface, or the macromolecules may by synthesized on the surface using light-activated or other synthetic reactions. Previous methods also include using printing techniques to produce such arrays. Some methods for producing arrays have been described in “Gene-Expression Micro-Arrays: A New Tool for Genomics”, Shalon, D., in Functional Genomics; Drug Discovery from Gene to Screen, IBC Library Series, Gilbert, S. R. & Savage, L. M., eds., International Business Communications, Inc., Southboro, Mass., 1997, pp 2.3.1.-2.3.8; “DNA Probe Arrays: Accessing Genetic Diversity”, Lipshutz, R. J., in Gilbert, S. R. & Savage, L. M., supra, pp 2.4.1.-2.4.16; “Applications of High-Throughput Cloning of Secreted Proteins and High-Density Oligonucleotide Arrays to Functional Genomics”, Langer-Safer, P. R., in Gilbert, S. R. & Savage, L. M., supra; Jordan, B. R., “Large-scale expression measurement by hybridization methods: from high-densities to “DNA chips”, J. Biochem. (Tokyo) 124: 251-8, 1998; Hacia, J. G., Brody, L. C. & Collins, F. S., “Applications of DNA chips for genomic analysis”, Mol. Psychiatry 3: 483-92, 1998; and Southern, E. M., “DNA chips: Analyzing sequence by hybridization to oligonucleotides on a large scale”, Trends in Genetics 12: 110-5, 1996.
Regardless of the technique, each microarray is individually and separately made, typically is used only once and cannot be individually precalibrated and evaluated in advance. Hence, one depends on the reproducibility of the production system to produce error-free arrays. Those factors have contributed to the high cost of currently produced biochips or microarrays, and have discouraged application of the technology to routine clinical use.
For scanning arrays, charged coupled device (CCD) cameras can be used. The cost of those devices has declined steadily, with suitable cameras and software now widely available. Such devices generally detect light sources or light absorbance. In one proposed variation, an array is located at the ends of a bundle of optical fibers with the nucleic acid or antibody/antigen attached to the other end of the optical fiber. Detection of fluorescence then may be performed through the optical fiber, see U.S. Pat. No. 5,837,196.
Fiber optical arrays can be produced in which glass or plastic fibers are aligned in parallel in such a manner that all remain parallel, and an optical image may be transmitted through the array. Parallel arrays also may be made of hollow glass fibers, and the array sectioned normal to the axis of the fibers to produce channel plates used to amplify optical images. Such devices are used for night vision and other optical signal amplification equipment. Channel plates have been adapted to the detection of binding reactions (U.S. Pat. No. 5,843,767) with the individual holes being filled after sectioning of the channel plate bundle, and discrete and separate proteins or nucleic acids being immobilized in separate groups of holes.
Hollow porous fibers have been used for dialysis of biological samples, for example, in kidney dialyzers and for water purification. Methods for aligning the fibers in parallel arrays, for impregnating the volume between the fibers with plastic, and for cutting the ends of such arrays have been described (see, for example, U.S. Pat. No. 4,289,623).
Immobilized enzymes have been prepared in fiber form from an emulsion as disclosed, for example, in Italy Pat. No. 836,462. Antibodies and antigens have been incorporated into solid phase fibers as disclosed in U.S. Pat. No. 4,031,201. A large number of other different immobilization techniques are known in the fields of solid phase immunoassays, nucleic acid hybridization assays and immobilized enzymes, see, for example, Hermanson, G. T., Bioconjugate Techniques. Academic Press, New York. 1995, 785 pp; Hermanson, G. T., Mallia, A. K. & Smith, P. K. Immobilized Affinity Ligand Techniques. Academic Press, New York, 1992, 454 pp; and Avidin-Biotin Chemistry: A Handbook. D. Savage, G. Mattson, S. Desai, G. Nielander, S. Morgansen & E. Conklin, Pierce Chemical Company, Rockford Ill., 1992, 467 pp.
Currently available biochips include only one class of immobilized reactant, and perform only one class of reactions. For many types of clinical and other analyses, there is a need for chips that can incorporate reactants immobilized in different ways in one chip.